Sketchatone

Sketchatone

Turn your drawing tablet into a MIDI strumming controller

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Common issues and solutions

Troubleshooting

This guide covers common issues and their solutions.

MIDI Issues

Notes Stick or Sustain Indefinitely

Symptoms:

  • Notes continue playing after you stop strumming
  • Notes don't turn off properly during rapid strumming
  • Hardware synthesizer plays sustained notes that never end

Cause: Some hardware synthesizers (especially when connected via USB MIDI) can't handle the rapid stream of MIDI messages during busy strumming. The MIDI buffer overflows, causing Note Off messages to be lost.

Solution: Add a delay between MIDI messages using midiInterMessageDelay:

{
  "midi": {
    "midiInterMessageDelay": 0.08
  }
}

Recommended values:

  • 0.08 (80ms) - Good starting point for most hardware synths
  • 0.05 (50ms) - Try if 80ms feels too sluggish
  • 0.1 (100ms) - Use if notes still stick with lower values
  • 0 (default) - No delay, maximum responsiveness

Note: This adds latency to MIDI output. Only use if experiencing stuck notes.

Tested with:

  • Roland Juno-DS88 (USB MIDI) - Works with 0.08
  • E-MU USB MIDI cables - May need adjustment

No MIDI Output

Symptoms:

  • No sound when strumming
  • MIDI monitor shows no messages

Solutions:

  1. Check MIDI port connection:

    # On Raspberry Pi (ALSA)
aconnect -l

# Look for your MIDI device and note the port number

  2. Verify config file:

    {
  "midi": {
    "midi_output_backend": "rtmidi",  // or "jack" for Zynthian
    "midi_output_id": 0  // Try different port numbers
  }
}

  3. Check available ports:

    • The server prints available MIDI ports on startup
    • Look for [RtMidi] Available MIDI output ports: in the console

  4. Test with virtual port: Set midi_output_id to null - this creates a virtual MIDI port you can connect to

MIDI Input Not Working

Symptoms:

  • Playing notes on external keyboard doesn't update strum notes in dashboard
  • No MIDI input messages received

Solutions:

  1. Check input port configuration:

    {
  "midi": {
    "midi_input_id": 0,  // Specific port, or null for all ports
    "midi_input_exclude": [
      "Midi Through",
      "RtMidi"
    ]
  }
}

  2. Verify port isn't excluded:

    • The server automatically excludes the output port to prevent feedback
    • Check the midi_input_exclude list
    • Remove your keyboard's port name if it's being excluded

  3. Test with aseqdump (Raspberry Pi):

    # List ports
aconnect -l

# Monitor a specific port (e.g., 28:0)
aseqdump -p 28:0

# Play notes on keyboard - you should see MIDI messages

Post-Installation Configuration

Setting Up MIDI Input (Optional)

Strumming should work right away after installation. However, if you want to use an external MIDI keyboard to change the notes being strummed (e.g., playing chords on a keyboard to update the strum pattern), you'll need to configure MIDI input.

Find available MIDI input ports:

# On Raspberry Pi (ALSA)
aconnect -l

# Look for your MIDI device in the output, e.g.:
# client 28: 'Juno-DS' [type=kernel,card=2]
#     0 'Juno-DS MIDI 1  '
#     1 'Juno-DS MIDI 2  '

The port number format is client:port, so in the example above, "Juno-DS MIDI 1" would be port 28:0.

Configure MIDI input:

Edit the config file:

sudo nano /opt/sketchatone/configs/config.json

Add or update the midi_input_id:

{
  "midi": {
    "midi_output_id": 0,
    "midi_input_id": 0,  // Set to your MIDI input port number
    "midi_input_exclude": [
      "Midi Through",
      "RtMidi"
    ]
  }
}

Restart the service:

sudo systemctl restart sketchatone

View logs to verify connection:

# Follow logs in real-time
sudo journalctl -u sketchatone -f

# Look for lines like:
# [RtMidi] Available MIDI input ports:
# [RtMidi]   0: Juno-DS MIDI 1
# ✓ MIDI input: Juno-DS MIDI 1

Tip: If you want to listen to all MIDI input ports (discovery mode), set midi_input_id to null:

"midi_input_id": null

Installation Issues

python-rtmidi Installation Fails

Symptoms:

  • Error during apt install ./sketchatone-*.deb
  • Message: "python-rtmidi install failed"

Solutions:

The installer now tries multiple methods automatically:

  1. First tries apt install python3-rtmidi (pre-compiled)
  2. Falls back to pip install python-rtmidi (compiles from source)

If both fail:

# Install build dependencies
sudo apt-get install -y python3-dev build-essential libasound2-dev

# Try manual install
pip3 install python-rtmidi

Performance Issues

High Latency / Sluggish Response

Causes:

  • midiInterMessageDelay set too high
  • System under heavy load
  • USB issues

Solutions:

  1. Reduce inter-message delay:

    {
  "midi": {
    "midiInterMessageDelay": 0  // Remove delay if notes aren't sticking
  }
}

  2. Check system load:

    top
# Look for high CPU usage

  3. Use JACK on Zynthian:

    • JACK provides lower latency than ALSA
    • Set "midi_output_backend": "jack"

Viewing Logs

Since Sketchatone runs as a systemd service, you can view logs using journalctl:

# View recent logs
sudo journalctl -u sketchatone

# Follow logs in real-time (like tail -f)
sudo journalctl -u sketchatone -f

# View logs since last boot
sudo journalctl -u sketchatone -b

# View last 50 lines
sudo journalctl -u sketchatone -n 50

# View logs with timestamps
sudo journalctl -u sketchatone --since "5 minutes ago"

Check service status:

sudo systemctl status sketchatone

This shows whether the service is running, recent log entries, and any errors.

See Also